In Utetheisa ornatrix (Lepidoptera, Arctiidae), the female mates
preferentially with larger males. Having a larger father results in
the eggs being more richly endowed with defensive pyrrolizidine
alkaloid (which the female receives from the male with the sperm
package, in quantity proportional to the male's body mass, and
passes on to the eggs); having a larger father also results in the
sons and daughters themselves being larger (body mass is heritable
in Utetheisa). We provide evidence herein that these consequences
enhance the fitness of the offspring. Eggs sired by larger
males are less vulnerable to predation (presumably because of
their higher alkaloid content), whereas sons and daughters, by
virtue of being larger, are, respectively, more successful in courtship
and more fecund. The female Utetheisa, therefore, by being
choosy, reaps both direct phenotypic and indirect genetic benefits.